Landforms/Geomorphology

"The size and morphology of coastal dunes is dependent on the complex interaction between controlling winds, sediment supply, and the geomorphology of the nearshore and beach environment."

The diagram on the right shows the beach-dune system [with] the nearshore zone back-beach environment and the formation of an incipient foredune and established foredune."

"Secondary dunes are the result of the subsequent modification of the "primary dune" by continued aeolian processes, and are generally located further inland, separated from nearshore processes (Davies 1980). The main secondary dunes include blowouts, parabolic dunes, and transgressive dunefields [image on the left and second right]."

"The wind flow structure in a blowout may be very complex and highly turbulent. Generally, the wind flow is locally accelerated through the blowout and a high speed jet is formed. Thus, wind speeds in the blowout are significantly greater than outside the blowout and this leads to high rates of sand erosion and transport (Carter et al. 1990, Hesp & Hyde 1996, Hesp 1999). Winds remove sand from the deflation basin and the lateral walls and transport it downwind. The erosional walls are then over-steepened and slumping occurs. This causes the erosional walls to retreat, widening the blowout and supplying sediment to the deflation basin, which is then subsequently transported to the depositional lobe. The wind flow is maximised up the axis of the blowout (middle of the deflation basin) towards the depositional lobe. It experiences rapid flow deceleration over the lobe crest, depositing sediment in a radial fashion over the depositional lobe [shown in the images on the right, left and second right]. Deflation basins tend to continue to erode until a base level such as water table level or a more consolidated surface is reached (e.g., old soil profiles, an indurated sediment layer), or a lag surface where coarser materials such as pebbles, shell, or pumice may have been concentrated. Many blowouts become larger over time and may evolve into parabolic dunes [see the two images on the right]."

The second image on the left is a model for the landforms that may occur as a glacier retreats or is melted. Landforms to be expected from a retreating glacier include an outwash plain, one or more terminal moraines from repeated retreats or meltings, recessional moraines (an earlier and surged over terminal moraine), kames, an esker, a drumlin field, and a pro-glacial lake in a ground moraine.

Theoretical geomorphology

Def. "the study of the character and origin of landforms" is called geomorphology.

Def. "the study of landforms, their classification, origin, development, and history" is called geomorphology.

A variety of landforms occasionally occur juxtaposed in a landscape. Theoretical geomorphology is an effort to explain or describe a common cause for these landforms.

Hypotheses

Main resource: Hypotheses

1. A landform may have more than one origin.

See also

• Antarctic continental shelves
• Arctic continental shelves
• Glaciology
• Mediterranean continental shelves
• North east American continental shelves
• North Sea continental shelves
• North west African continental shelves
• South east African continental shelves
• South east Asian continental shelves
• South west African continental shelves
• West American continental shelves
• West European continental shelves

External links

• Bathymetry and Global Relief of Earth
• NASA's Earth Observatory Glossary
• NOAA's National Ocean Service
• NOAA's Ocean Explorer